1. Field of the Invention
The present invention is related to a light guide for endoscopes, that is, a light guide that propagates light therethrough such that portions which are observed with an endoscope are illuminated.
2. Description of the Related Art
Conventionally, endoscopes are in wide use to observe and perform surgical procedures on portions within body cavities of humans. Flexible light guides for illuminating the observed portions of subjects are employed in these endoscopes. Note that in cases that surgical procedures are performed on portions, observation thereof is necessary. Therefore, portions on which surgical procedures are performed will also be referred to as “observed portions” in the present specification.
At least a portion of this type of light guide is generally constituted by a plurality of thin multi mode optical fibers which are bundled, to impart flexibility thereto. Japanese Unexamined Patent Publication No. H6 (1994)-296584 discloses an example of a light guide for endoscopes configured in this manner. This light guide for endoscopes receives illuminating light beam, by the illuminating light beam being emitted from an illuminating light source, focused, then irradiated on a first end facet of the light guide. The illuminating light beam propagates through the light guide and is emitted from a second end facet to illuminate an observed portion.
An example of a conventional light guide for endoscopes 5 is illustrated in FIG. 7. In FIG. 7, reference numeral 11 denotes a plurality of multi mode optical fibers, and reference numeral 12 denotes a filling adhesive for fixing the multi mode optical fibers 11 in a bundle so as to form a connector portion. Note that the filling adhesive 12 is generally housed within a cylindrical connector housing. Reference numeral 6 of FIG. 7 denotes an illuminating light source for emitting an illuminating light beam 7, reference numeral 8 denotes a focusing optical system for focusing the illuminating light beam 7 and causing it to enter the plurality of multi mode optical fibers 11 from a side towards first end facets (light input end facets) thereof, and reference numeral 9 denotes an optical element which is provided in close contact with the second end facets (light output end facets) of the multi mode optical fibers 11.
In light guides for endoscopes, in which the end portions that function as light input portions are constituted by a plurality of thin optical fibers as described above, there are problems that heat is easily generated at the light input portions, and that the heat degrades the optical fibers.